With days to go before he takes the stand against Martha Stewart, her broker’s ex-assistant has been holding down a new job in a Chelsea art gallery, chatting with pals and making dinner plans.

Doug Faneuil, the man who could send the domestic diva to jail, started as an assistant at the Debs & Co. contemporary art gallery on 26th Street three weeks ago in a bid to get his shattered life back on track. The gallery is partly owned by a close pal.

Scruffily dressed in blue jeans, a brown sweater, sneakers and red scarf, Faneuil was relaxed and in good spirits yesterday despite being on the brink of what could be a courtroom mauling.

Faneuil, who sold almost 4,000 ImClone shares for Stewart on Dec. 27, 2001, is set testify that Stewart and her broker, his boss, Peter Bacanovic, lied to feds investigating them for insider trading. Stewart and Bacanovic’s lawyers plan to say the 28-year-old lacks credibility. Faneuil is expected to be one of two government witnesses are due to take the stand Tuesday when the explosive trial gets under way following a week of jury selection.